The present invention relates to an optical information recording and reproducing apparatus for recording or reproducing signals on optical discs by using a light spot.
In optical information recording and reproducing apparatuses, typified by DVD-R and DVD-RAM apparatuses, a light spot of a diameter of about 0.5 xcexcm is applied to information tracks formed at a pitch of 0.74 xcexcm on a disk to record and reproduce information. When the light spot is applied to the face of the disk, focus control is carried out so that the light spot traces the disk face at an accuracy of about xc2x10.5 xcexcm or less in a direction perpendicular to the disk face. In addition, tracking control is carried out so that the tracking displacement of the light spot from the information track is about xc2x10.1 xcexcm or less.
A one-beam push-pull system is available as a conventional method of making a light spot to follow tracks.
A conventional optical information recording and reproducing apparatus by use of this one-beam push-pull system will be described below referring to FIG. 41. FIG. 41 is a block diagram showing the configuration of the above-mentioned conventional optical information recording and reproducing apparatus. In FIG. 41, a disk 2 having helical or concentric information tracks 1, shown magnified, is configured so as to be rotated by a spindle motor 3. Recording and reproduction on the information tracks 1 of the disk 2 are carried out by an optical pickup 4. The optical pickup 4 is provided with a semiconductor laser 5, a collimator lens 6, a beam splitter 7, an object lens 8, a two-part split PD (photodetector) 9 and a tracking actuator 10 used as a lens movement means. The tracking actuator 10 comprises a coil 11 secured to the object lens 8 and a magnet 13 secured to the housing of the optical pickup 4, and the coil 11 is connected to the magnet 13 via a spring 12. When a current flows through the coil 11, an electromagnetic force is generated between the coil 11 and the magnet 13, and the object lens 8 moves in the tracking direction. When the optical pickup 4 is not operating, that is, when no input signal is supplied to the tracking actuator 10, the object lens 8 is designed to stop at the neutral position of the optical pickup 4.
A tracking error detection circuit 14 generates a tracking error signal 101, i.e. the displacement amount of the object lens 8 from the center of the information tracks 1, on the basis of the difference between the outputs of the PD sections of the two-part split PD, and outputs the signal to a tracking control circuit 15. The tracking control circuit 15 outputs a tracking drive signal 103 to a tracking drive circuit 16 on the basis of the tracking error signal. The tracking drive circuit 16 supplies a current depending on the tracking drive signal 103 to the coil 11 of the tracking actuator 10. This circuit loop for the tracking control is referred to as a tracking control loop 201.
Concrete operations of the optical information recording and reproducing apparatus will be described next. The light beam emitted from the semiconductor laser 5 is made parallel light by the collimator lens 6 and converged to the information track 1 of the disk 2 through the beam splitter 7 and the object lens 8. By using part of the light reflected from the disk 2, focus control for moving the object lens 8 vertically is carried out so that the focus position of the light beam focused by the object lens 8 meets the face of the disk 2 at all times. However, the focus control is not described in detail since it does not directly relate to the present invention.
Part of the light reflected from the disk 2 enters the two-part split PD 9 through the object lens 8 and the beam splitter 7. The two-part split PD 9 outputs voltages indicating the amounts of light detected by the respective PD sections. The tracking error detection circuit 14 calculates the difference between the outputs of the two-part split PD 9 and outputs the tracking error signal 101 indicating the positional displacement amount between the focus of the light beam and the information track 1 to the tracking control circuit 15. By the operation of the tracking control loop 201, the tracking control circuit 15 outputs the tracking drive signal 103 to the tracking drive circuit 16 so that the amplitude of the tracking error signal 101 becomes zero, that is, so that the light beam positions at the center of the information track 1. The tracking drive circuit 16 flows a current through the coil 11 to generate an electromagnetic force thereby to move the object lens 8. With this configuration, even if the disk 2 is eccentric, the object lens 8 can be controlled so that the light spot follows the center position of the information track 1 during the rotation of the optical disk 2.
FIG. 42 is a graph showing the change of the tracking error signal with respect to time at a moment when the tracking control loop 201 is switched from its OFF state (a state wherein the tracking control loop 201 does not operate) to its ON state (a state wherein the tracking control loop 201 operates). When the tracking control loop 201 is in the OFF state, no drive force is applied to the tracking actuator 10 shown in FIG. 41; therefore, the object lens 8 is stationary at the neutral position of the optical pickup 4. If there is an eccentricity caused by the spindle motor 3 on which the disk 2 is mounted, or if the disk 2 itself has a slight eccentricity, the information track 1 also has an eccentricity with respect to the rotation center. Therefore, the information track 1 crosses the focus position of the object lens 8, and the tracking error signal 101 having a sine waveform is output in synchronization with the rotation of the disk 2. When the tracking control loop 201 is set the ON state, the object lens 8 is controlled so that the light spot follows the center position of the information track 1 by the operation of the tracking control loop 201 as described above, whereby the amplitude of the tracking error signal 101 becomes nearly zero.
In the configurations shown in the above-mentioned FIGS. 41 to 44, if the center of the object lens 8 is displaced from the neutral position of the optical pickup 4 because of some reasons, the center of the object lens 8 is displaced from the center of the,light beam emitted from the semiconductor laser 5, thereby causing an offset. As a result, the distribution of the incident light from the disk 2 to the two-part split PD 9 varies, and the waveform of the tracking error signal 101 changes, whereby the follow-up control for the information track becomes unstable.
A first problem owing to the displacement of the center of the object lens 8 is an offset in the tracking error signal 101. FIG. 43(a) is a side view showing the positional relationship between the light beam of the reflected light and the two-part split PD at the time when the optical axis of the object lens 8 is displaced from the center position of the light beam. When the object lens 8 is displaced from the position indicated in solid lines to the position indicated in two-dot chain lines, the center position A of the light beam is displaced to position B; as a result, the center of the light beam reflected by the optical disk 2 and made incident upon the two-part split PD is displaced by distance x. Consequently, regarding the amounts of incident light at the detection areas a and b of the two-part split PD 9, the amount of incident light in the detection area a is less than that in the detection area b, whereby an imbalance occurs therebetween. The tracking error detection circuit 14 detects the tracking error signal 101 by calculating the difference between the amounts of light at the detection areas a and b. Therefore, if an imbalance occurs between the amounts of light in the detection areas a and b of the two-part split PD 9, an offset occurs in the tracking error signal.
A second problem is the decrease of the amplitude of the tracking error signal 101. In FIG. 43(a), if the position of the object lens 8 is displaced, the light beam of the reflected light is away from the detection area of the two-part split PD 9 by distance y, whereby the total amount of the incident light decreases.
FIG. 43(b) is a graph showing the relationship between the displacement amount x of the object lens 8 and the tracking error signal 101 output from the tracking error detection circuit 14 at the time when the object lens 8 crosses the information tracks 1. As the displacement distance x of the object lens 8 increases, the off set of the amplitude center increases, and the amplitude of the tracking error signal decreases.
FIG. 43(c) is a graph showing the change of the tracking error signal 101 with respect to time at a moment when the tracking control loop 201 is switched from the OFF state to the ON state in the case that the object lens 8 causes a positional displacement. The case wherein the object lens 8 causes a positional displacement is indicated in a solid line, and the case wherein the object lens 8 does not cause any positional displacement is indicated in a two-dot chain line. Since the case wherein the object lens 8 does not cause any positional displacement is similar to that shown in FIG. 42, which is applied in a similar manner, its explanation is omitted. When the tracking control loop 201 shown in FIG. 41 is in the OFF state, the tracking error signal 101 is output in a sine waveform as indicated in a two-dot chain line in FIG. 43(c). However, if the object lens 8 has a positional displacement, an offset indicated in a one-dot chain line occurs at the center of the amplitude of the tracking error signal 101 depending on the displacement amount as indicated in the solid line in FIG. 43(c), and the amplitude decreases.
When the tracking control loop 201 is set at the ON state, the amplitude of the tracking error signal 101 becomes nearly zero because of the operation of the control loop. However, since the center of the information track 1 corresponds to the position indicated in the one-dot chain line, if control is carried out so that the amplitude of the tracking error signal 101 becomes zero, the object lens 8 is made to follow the position displaced from the center of the information track 1, thereby causing an off-track (the displacement between the object lens 8 and the center of the track). Furthermore, since the amplitude of the tracking error signal 101 decreases depending on the positional displacement amount of the object lens 8, the detection gain (the ratio of the off-track amount and the amplitude of the tracking error signal 101) of the tracking error detection circuit 14 becomes smaller, and the gain of the circuit of the tracking control loop 301 also becomes smaller, whereby control performance lowers. If the object lens 8 is displaced as described above, it is necessary to carry out both the offset correction and amplitude correction of the tracking error signal.
A third problem is the occurrence of the offset and an amplitude variation of the tracking error signal 101 not only when the object lens 8 is displaced but also when the optical axis of the object lens 8 is not held perpendicular to the disk face but tilted in the tangent direction of the track.
FIG. 44(a) is a side view showing the positional relationship between the light beam of the reflected light and the two-part split PD 9 at the time when the optical disk 2 is tilted with respect to the optical axis of the optical pickup 4. If the optical disk 2 is displaced by a tilt angle z from state C wherein the optical axis is perpendicular to the optical disk 2 as indicated in solid lines to state D indicated in two-dot chain lines, the light beam reflected by the optical disk 2 and made incident upon the two-part split PD 9 is displaced to the position indicated in the two-dot chain lines. Therefore, regarding the light amounts at the detection areas a and b of the two-part split PD, the light amount in the detection area a becomes less than that in the detection area b, whereby an imbalance occurs. Consequently, as shown in FIG. 44(b) (sic FIG. 44(b)) and just as in the case when the object lens 8 is displaced, the tracking error signal 101 output from the tracking error detection circuit 14 causes an offset, the amplitude decreases, and off-track occurs, thereby lowering control performance. Therefore, it is necessary to correct the tracking error signal 101 by using not only the positional displacement information of the object lens 8 but also the tilt angle information of the disk 2.
The present invention is first intended to solve the above-mentioned first to third problems thereby to greatly improve the stability of the tracking control.
If the optical axis of the object lens is not perpendicular to the disk face but tilted in a direction perpendicular to the tangent line of the information track when the light spot is applied to the disk, the light spot is also applied to an adjacent track, and the information of the adjacent track is mixed therein. Therefore, it is necessary to carry out tilt control so that the tilt angle of the optical axis from a direction perpendicular to the disk face becomes zero.
The tilt control for another conventional optical information recording and reproducing apparatus will be described below referring to drawings. FIG. 45 is a block diagram showing the configuration of the conventional optical information recording and reproducing apparatus.
In FIG. 45, a disk 301 is disposed above (upward from the paper face) a mechanism section including an optical pickup 302 and a lead screw 305; for ease in understanding, the above-mentioned mechanism section is indicated in solid lines, and the disk 301 is indicated in a one-dot chain line. A light beam 302A is applied through an object lens 303 installed on the optical pickup 302 to the information tracks formed concentrically or helically on the disk 301 to record and reproduce information. A lead rack 304 is secured to the side face of the optical pickup 302. The lead rack 304 has a projection 304A, and the projection 304A is movably fitted in the helical groove of the lead screw 305. An end of the lead screw 305 is directly connected to the motor shaft 306A of an optical pickup movement motor 306. One ends of two lead shafts 307 for holding the optical pickup 302 so as to be movable in the radial direction of the disk 301 are installed in lead shaft holders 308, and the other ends thereof, bent in the L shape, are inserted in the holes of tilt cams 309. As shown in FIG. 46 and FIG. 47(a), a tilt sensor 310 installed on the lead rack 304 has a light source 327 and a two-part split PD 326 used as a photodetector, a light beam 327A is applied from the light source 327 to the face of the disk 301, and a light beam 327B reflected by the disk 301 is detected by the two-part split PD 326. The tilt sensor 310 outputs a signal indicating xe2x80x9cthe tilt angle of the optical axis of the light beam 327A from a direction perpendicular to the face of the disk 301xe2x80x9d (hereafter simply referred to as a tilt angle). The signal indicating the tilt Angle is treated by the tilt error detection circuit 311 of FIG. 45, and a tilt error signal 401 corresponding to the tilt angle is output.
A tilt control circuit 312 supplies a control signal to a tilt drive circuit 313 so that the level of the tilt error signal 401 becomes zero thereby to control a tilt motor 314 for rotating a tilt shaft 315 directly connected to the shaft of the tilt motor and the tilt cams 309 eccentrically installed on the tilt shaft 315.
Operations will be described in detail next. The light beam 302A emitted from the optical pickup 302 is focused on the information track 331 of the disk 301 by the object lens 303. The optical pickup 302 uses a part of the light reflected by the disk 301 to carry out focus control wherein the object lens 303 is moved in a direction perpendicular to the disk 301 so that the focus position of the light beam 302A focused by the object lens 303 meets the disk 301 at all times and to carry out tracking control wherein the object lens 303 is moved in a direction perpendicular to the information track 331 so that the light beam 302A is positioned at the center of the information track. Since the focus control and the tracking control do not directly relate to the present invention, their detailed explanations are omitted. To carry out recording or reproduction at a target track, the lead screw 305 is rotated by the pickup movement motor 306, whereby the optical pickup 302 is moved in the radial direction of the disk 301 via the lead rack 304 having the projection 304A fitted in a groove helically formed in the lead screw 305. The tilt sensor 310 installed on the lead rack 304 detects the tilt of the light beam 302A with respect to the disk face, and the tilt error detection circuit 311 generates the tilt error signal 401 and outputs the signal to the tilt control circuit 312.
The tilt control circuit 312 outputs a drive command to the tilt drive circuit 313 so that the optical axis of the light beam 302A becomes perpendicular to the face of the disk 301 and so that the level of the tilt error signal 401 becomes zero. By using the drive command, the tilt drive circuit 313 flows a current to the tilt motor 314 to rotate it. The tilt motor 314 rotates the tilt cams 309 via the tilt shaft 315. As a result, the lead shafts 307 are rotated with the lead shaft holders 308 used as fulcrums thereby to tilt the optical pickup 302, the lead rack 304 and the tilt sensor 310. Even if the disk 301 is tilted in this configuration, control is made possible by controlling the tilt of the optical pickup 302 so that the light beam 302A output from the optical pickup 302 is applied in a direction perpendicular to the face of the disk 301 at all times.
FIG. 46 is a plan view showing the concrete configurations of the tilt sensor 310 and the tilt error detection circuit 311. As shown in FIG. 46, the two-part split PD 326 of the tilt sensor 310 is split into two parts along the tangent line 331A of the information tracks 331 recorded concentrically or helically on the disk 301. The optical axis of the light beam 327A from the light source 327 is made perpendicular to the tangent line 331A of the information track 331 on the disk 301 (in other words, parallel with the optical axis of the light beam of the optical pickup 302), and is disposed on the extension line of the tangent line 331A overlapping the split line of the two-part split PD 326 so that the light reflected from the disk 301 enters the center of the two-part split PD 326. The tilt error detection circuit 311 has a subtraction circuit 328 for obtaining the difference between the outputs of the PD sections 326a and 326b of the two-part split PD 326.
The concrete operation of the tilt control will be described by using FIGS. 47 and 48. FIG. 47(b) is a plan view showing the position of the light beam 327B of the reflected light incident on the two-part split PD 326 at the time when the light beam 327A emitted from the light source 327 of the tilt sensor 310 is applied to the disk 301. As shown in FIG. 48(a), if the disk 301 is tilted by tilt angle z from the state wherein the light beam 327A perpendicularly enters the disk 301 indicated in solid lines 301A to the state wherein the disk 301 is indicated in two-dot chain lines (sic two-dot chain lines) 301B, the light beam 327B reflected by the disk 301 and made incident upon the two-part split PD 326 is displaced to the position indicated in the dotted line in FIG. 4b(b). As a result, the light amount at the PD section 326b of the two-part split PD 326 becomes less than the light amount at the PD sectional 326a, whereby the output levels of the PD sections 326a and 327b of the two-part split PD 326 change as shown in the top and intermediate graphs of FIG. 48(b) respectively. The difference between the two output levels of the PD sections 326a and 326b is obtained by the subtraction circuit 328 of the tilt detection circuit 310, whereby the tilt error signal 401 shown in the bottom graph of FIG. 48(b) is obtained. In this way, the level of the tilt error signal 401 output from the tilt error detection circuit 310 changes depending on the tilt angle of the disk 301 indicated on the abscissa. When the light beam 327A is made incident perpendicularly upon the face of the disk 301, the output level of the PD section 326a is equal to that of the PD section 326b, and the level of the tilt error signal 401 becomes zero. By controlling the tilt of the integrated unit of the optical pickup 302 and the tilt sensor 310 so that the level of the tilt error signal 401 becomes zero, the light beam 327A output from the optical pickup 302 is controlled so as to be applied perpendicularly to the face of the disk 301. If the level of the tilt error signal 401 is not zero even when the light beam 327A is made incident perpendicularly upon the face of the disk 301, this state is referred to as xe2x80x9can offset has occurred,xe2x80x9d and this level is referred to as xe2x80x9can offset amount.xe2x80x9d
In the conventional example shown in the above-mentioned FIG. 45, in the case when an offset occurs in the tilt error signal 401 detected by the tilt sensor 310 because of some reasons, if control is carried out so that the level of the tilt error signal 401 becomes zero, the optical axis of the optical pickup 302 is tilted by an angle corresponding to the amount of the offset with respect to a plane perpendicular to the disk 301, whereby the accuracy of the tilt control becomes low. The causes of offset occurrence will be described below.
As the optical pickup 302 is moved, the lead rack 304 may be deformed and the tilt sensor 310 may be tilted. Because of this tilt, the optical axis of the light beam 302A output from the optical pickup 302 is not held parallel with the optical axis of the outgoing light 327A from the light source 327 of the tilt sensor 310, and an offset occurs in the tilt error signal 401. FIG. 49 is a side view showing forces exerted on the lead rack 304 at the time when the lead screw 305 rotates. In FIG. 49, the projection 304A is formed on the side face of the lead rack 304 and fitted in the groove 305A of the lead screw 305. When the lead screw 305 is rotated in the direction indicated by arrow W, the groove 305A of the lead screw 305 moves apparently in the direction indicated by arrow C, and the lead rack 304 also moves in the direction indicated by the arrow C. At this time, a force is also applied to the lead rack 304 via the groove 305A in the direction indicated by arrow D. Therefore, the lead rack 304 is rotated clockwise as indicated in one-dot chain lines and slightly displaced in the direction indicated by arrow E. By this rotation and displacement, the tilt sensor 310 installed on the lead rack 304 shown in FIG. 45 is tilted, and the optical axis of the light beam 302A output from the optical pickup 302 does not become parallel with the optical axis of the outgoing light 327A of the light source 327 of the tilt sensor 310. As a result as indicated in one-dot chain lines in the graphs of FIG. 50(a) (sic FIG. 50(a)), the level of the output signal from the two-part split PD 326 of the tilt sensor 310 is shifted, and an offset occurs in the tilt error signal 401. If the lead screw 305 is rotated in the direction opposite to the direction of the arrow W, the lead rack 304 is displaced in the direction opposite to the direction of the arrow E, thereby causing an offset in the direction opposite to that in the above-mentioned case as indicated in two-dot chain lines in the graphs of FIG. 50(a). The solid lines in the graphs of FIG. 50(a) show the respective outputs at the time when the lead rack 304 is not displaced.
Furthermore, an offset also occurs owing to a temperature change at the peripheral sections of the tilt sensor 310 and the lead rack 304.
If the temperatures of the tilt sensor 310 and the lead rack 304 change, an imbalance occurs between the detection sensitivity levels of the PD sections 326a and 326b of the two-part split PD 326 inside the tilt sensor 310, whereby an offset occurs in the tilt error signal 401. In addition, the lead rack 304 itself is deformed, and the optical axis of the optical pickup 302 does not becomes parallel with the optical axis of the light source 327 of the tilt sensor 310, whereby an offset occurs in the tilt error signal 401.
The magnitude of the offset of the tilt error signal 401 may change depending on the reflectivity of the disk 301. The graphs of FIG. 50(b) show the relationship between the reflectivity of the disk 301 and the tilt error signal output 401 at the time when an offset occurs in the tilt error signal. 401. The solid lines of FIG. 50(b) indicate the output signals of the PD sections 326a and 326b of the two-part PD 326 and the tilt error signal 401 at the time when the reflectivity of the disk is 30%. When the reflectivity of the disk 301 becomes 50%, the detection levels of the PD sections 326a and 326b increase as the reflectivity increases as shown in the one-dot chain lines of FIG. 50(b), and the output level with respect to the tilt angle of the disk 301 also increases. Therefore, the level of the tilt error signal 401 with respect to the tilt angle of the disk 301 increases, and the offset of the tilt error signal 401 at the time when the tilt angle of the disk 301 is zero increases as the reflectivity increases.
In the case when the disk 301 is a recordable optical disk, problems described below are caused. FIG. 51 shows the distribution of the light intensity of the light beam of the optical pickup 302, the states of pits formed in the disk and the relationship of reproduced signals read by the optical pickup 302. The light reflectivity of the pit section formed by recording is lower than that of other sections. This difference in the reflectivity is detected based on a level difference in the amount of the reflected light of the light beam emitted from the optical pickup 302. FIGS. 51(a) and (b) are graphs showing the distribution of the light intensity in the tracking direction TD of the light beam output from the optical pickup 302. First, as shown in FIG. 51(a), the case wherein the distribution of the intensity of the light beam is symmetrical with respect to the optical axis OC of the light beam will be explained.
When the light sensitivity levels of the areas A and B of the disk 301 irradiated with the light beam in the vicinity of the optical axis OC are equal to each other, and when a single data (data having a pit length being equal to the length between pits) is recorded on the optical disk 301, pits P symmetrical with respect to the center line TC of the track are recorded as shown in FIG. 51(c). When the recorded single data is read by the optical pickup 302, reflected light having a low level is obtained while the light beam passes through the pits P, and reflected light having a high level is obtained at areas having no pits. An RF signal, whose level changes depending on the presence or absence of the pits P, is obtained from this reflected light as shown in FIG. 51(d). When this RF signal is binarized by slicing the RF signal at the center value SL of the RF signal, and when it is assumed that the level of the signal not less than the center value SL is Hi and the level less than the center value is Low, a binary RF signal shown in FIG. 51(e) is obtained. When a single data is recorded, time TH during which the RF signal is Hi becomes equal to time TL during which the RF signal is Low.
When the light sensitivity of the above-mentioned area A is lower than the light sensitivity of the area B for example, the recorded pits P do not become symmetrical with respect to the track center line TC but become deviated as shown in FIG. 51(f). For example, when the distribution of the intensity of the light beam is not symmetrical with respect to the optical axis OC of the light beam but deviated rightward in the graph of FIG. 51(b), even if the light sensitivity levels of the areas A and B of the disk 301 are equal to each other, the recorded pits P become deviated shape with respect to the track center line TC as shown in FIG. 51(f). When the pits P deviated with respect to the track center line TC as described above are read by the optical pickup 302, an RF signal shown in FIG. 51(g) is obtained. The reasons are as follows: since the light beam passes through the ends of the pits P, the difference between the level at the time of passing through the pits P and the level at the time of passing through the no-pit area becomes small. In addition, depending on the deviation from the track center line TC of the pits P, the timing when the light beam arrives at the pits P is delayed. When the RF signal of FIG. 51(g) is inverted into a binary value by slicing it at the center value SL of the RF signal, a binary RF signal is obtained as shown in FIG. 51(h); however, the Hi time does not become equal to the Low time, but the time TH becomes longer than the time TL. As a result, reproduced data becomes different from the recorded single data. In this way, the pits P deviated with respect to the track center line TC are not detected properly at the time of reproduction.
The deviation in the intensity of the light beam shown in FIG. 51(b) differs depending on the intensity of the outgoing light of the light beam. For example, the distribution of the light intensity at the time of a high intensity during recording is indicated in a dot line and the distribution of the light intensity at the time of a low intensity during reproduction is indicated in a solid line in FIG. 51(i) (sic FIG. 51(i)). This is because when the intensity of the outgoing light of the light beam becomes high, the wavelength of the outgoing light changes depending on the change in the temperature around the optical pickup, or strains occur at the mechanism section of the optical pickup. In addition, the deviation of the distribution of the intensity of the light beam may occur depending on changes in various environmental conditions, such as the temperature, humidity and pressure around the apparatus. This is because strains occur at the mechanism sections of the apparatus owing to changes in the environmental conditions. Strains may also occur at the mechanism sections of the apparatus because of changes with the passage of time. In addition, the reflectivity at the face of the optical disc and the reflectivity at the pits P are different depending on the manufacturer of the disk. The amplitude RFA of the RF signal changes depending on these differences in the reflection, whereby the time TH may become unequal to the time TL in some cases. Furthermore, in order to increase the density of recording capacity, it is necessary to reduce the distance between the tracks on the disk or to decrease the width of the recording pits P; this tends to further increase errors at the time of reproduction.
An optical information recording and reproducing apparatus in accordance with the present invention comprises a disk on which information is recorded along tracks, an optical pickup, having an object lens, for applying a light spot to the recording face of the above-mentioned disk, a tracking error detection section for detecting the positional displacement amount between the above-mentioned light spot and an information track recorded on the above-mentioned optical disk and for outputting a tracking error signal corresponding to the positional displacement amount, a lens movement section for moving the object lens of the above-mentioned optical pickup in a direction crossing the above-mentioned information tracks, a tracking control section, including a compensation calculation section, for controlling the above-mentioned lens movement section depending on the above-mentioned tracking error signal, an object lens displacement estimation section for estimating the displacement of the optical axis of the object lens from the center position of the light beam of the above-mentioned optical pickup on the basis of the output of the above-mentioned compensation calculation section, an offset detection section for detecting the offset of the above-mentioned tracking error signal, a memory section for storing the output of the above-mentioned offset detection section and the output of the above-mentioned object lens displacement estimation section as a pair, and an offset correction section for outputting the output of the above-mentioned offset detection section corresponding to the output of the above-mentioned object lens displacement estimation section from the above-mentioned memory section and for correcting the offset of the above-mentioned tracking error signal.
From the output of the offset detection section and the output of the object lens displacement estimation section stored as a pair in the memory section, the output of the offset detection section corresponding to the output of the object lens displacement estimation section is obtained. A tracking signal is obtained from the obtained output, and the offset of the tracking error signal is corrected. As a result, the positional displacement of the object lens of the optical pickup is corrected, whereby the light spot can be positioned properly on the track of the disk.
An optical information recording and reproducing apparatus in another aspect of the present invention comprises a disk on which information is recorded along tracks, an optical pickup, having an object lens, for applying a light spot to the recording face of the above-mentioned disk, a tracking error detection section for detecting the positional displacement amount between the above-mentioned light spot and an information track recorded on the above-mentioned optical disk and for outputting a tracking error signal corresponding to the positional displacement amount, a lens movement section for moving the object lens of the above-mentioned optical pickup in a direction crossing the above-mentioned information tracks, a tracking control section, including a compensation calculation section, for controlling the above-mentioned lens movement section depending on the above-mentioned tracking error signal, an object lens displacement estimation section for estimating the displacement of the optical axis of the object lens from the center position of the light beam of the above-mentioned optical pickup on the basis of the output of the above-mentioned compensation calculation section, an amplitude detection section for detecting the amplitude of the above-mentioned tracking error signal, a memory section for storing the output of the above-mentioned amplitude detection section and the output of the above-mentioned object lens displacement estimation section so as to correspond to each other, and an amplitude correction section for outputting the output of the above-mentioned amplitude detection section corresponding to the output of the above-mentioned object lens displacement estimation section from the above-mentioned memory section and for correcting the amplitude value of the above-mentioned tracking error signal.
From the output of the amplitude detection section and the output of the object lens displacement estimation section stored so as to correspond to each other in the memory section, the amplitude value of the tracking error signal corresponding to the output of the object lens displacement estimation section is obtained. The tracking error signal is corrected by using the obtained amplitude value. As a result, the positional displacement of the object lens of the optical pickup is corrected, whereby the light spot can be positioned properly on the track of the disk.
An optical information recording and reproducing apparatus in other aspect of the present invention comprises a disk on which information is recorded along tracks, an optical pickup, having an object lens, for applying a light spot to the recording face of the above-mentioned disk, a tracking error detection section for detecting the positional displacement amount between the above-mentioned light spot and an information track recorded on the above-mentioned optical disk and for outputting a tracking error signal corresponding to the positional displacement amount, a lens movement section for moving the object lens of the above-mentioned optical pickup in a direction crossing the above-mentioned information tracks, a tracking control loop for controlling the above-mentioned lens movement section depending on the above-mentioned tracking error signal, an object lens displacement estimation section for estimating the displacement of the optical axis of the object lens from the center position of the light beam of the above-mentioned optical pickup, and a tracking correction control loop for controlling the above-mentioned lens movement section depending on the displacement amount of the optical axis of the object lens estimated by the above-mentioned object lens displacement estimation section.
In the tracking control loop, the lens movement section is controlled depending on the tracking error signal; in the tracking correction control loop, the lens movement section is controlled depending on the displacement amount of the optical axis of the object lens. As a result, the tracking error is corrected, and the displacement of the optical axis of the object lens is corrected.
An optical information recording and reproducing apparatus in other aspect of the present invention comprises a disk on which information is recorded along tracks, an optical pickup, having an object lens, for applying a light spot to the recording face of the above-mentioned disk, a tracking error detection section for detecting the positional displacement amount between the above-mentioned light spot and an information track recorded on the above-mentioned optical disk and for outputting a tracking error signal corresponding to the positional displacement amount, a lens movement section for moving the object lens of the above-mentioned optical pickup in a direction crossing the above-mentioned information tracks, a tracking control section for controlling the above-mentioned lens movement section depending on the above-mentioned tracking error signal, an object lens displacement detection section for detecting the displacement of the optical axis of the object lens from the center position of the light beam of the above-mentioned optical pickup, an offset detection section for detecting the offset of the above-mentioned tracking error signal, a tilt detection section for detecting the tilt amount of the light beam of the above-mentioned optical pickup with respect to the above-mentioned disk face in a direction perpendicular to the information track, a memory section for storing the output of the above-mentioned offset detection section, the output of the above-mentioned object lens displacement detection section and the output of the above-mentioned tilt detection section so as to correspond to one another, and an offset correction section for outputting the output of the above-mentioned offset detection section corresponding to the output of the above-mentioned object lens displacement detection section and the output of the above-mentioned tilt detection section from the above-mentioned memory section and for correcting the offset of the above-mentioned tracking error signal.
From the output of the offset detection section, the output of the object lens displacement estimation section and the output of the tilt detection section stored so as to correspond to one another in the memory section, the output of the offset detection section corresponding to the output of the object lens displacement estimation section and the output of the tilt detection section is obtained. A tracking signal is obtained from the obtained output, and the offset of the tracking error signal is corrected.
An optical information recording and reproducing apparatus in other aspect of the present invention comprises a disk on which information is recorded, an optical pickup, having an object lens, for applying a light spot to the recording face of the above-mentioned disk, a tracking error detection section for detecting the positional displacement amount between the above-mentioned light spot and an information track recorded on the above-mentioned optical disk and for outputting a tracking error signal corresponding to the positional displacement amount, a lens movement section for moving the object lens of the above-mentioned optical pickup in a direction crossing the above-mentioned information tracks, a tracking control section for controlling the above-mentioned lens movement section depending on the above-mentioned tracking error signal, an object lens displacement detection section for detecting the displacement of the optical axis of the object lens from the center position of the light beam of the above-mentioned optical pickup, a tilt detection section for detecting the tilt amount of the light beam of the above-mentioned optical pickup with respect to the above-mentioned disk face in a direction perpendicular to the information track, an amplitude detection section for detecting the amplitude of the above-mentioned tracking error signal, a memory section for storing the output of the above-mentioned amplitude detection section, the output of the above-mentioned object lens displacement detection section and the output of the above-mentioned tilt detection section so as to correspond to one another, an offset correction section for outputting the output of the above-mentioned amplitude detection section corresponding to the output of the above-mentioned object lens displacement detection section and the output of the above-mentioned tilt detection section from the above-mentioned memory section and for correcting the amplitude value of the tracking error signal of the above-mentioned tracking error detection section.
From the output of the amplitude detection section, the output of the lens displacement detection section and the output of the tilt detection section stored in the memory section, the amplitude value of the tracking error signal corresponding to these is corrected.
In order to record or reproduce information on the information tracks of a disk, an optical information recording and reproducing apparatus in accordance with the present invention from another point of view comprises an optical pickup for applying a light spot to the recording face of the above-mentioned disk via an object lens, a pickup movement section having a pickup movement motor for moving the above-mentioned optical pickup in a direction crossing the information tracks on the above-mentioned disk, a movement direction detection section for detecting the movement direction of the above-mentioned optical pickup, a tilt error detection section for detecting the tilt of the optical axis of the light beam of the above-mentioned optical pickup with respect to the above-mentioned disk face and for outputting the tilt as a tilt error signal, a tilt drive section for tilting the above-mentioned optical pickup and the above-mentioned tilt error detection section as an integrated unit, a tilt control section for controlling the above-mentioned tilt drive section depending on the above-mentioned tilt error signal, an offset detection section for detecting the offset of the above-mentioned tilt error signal, a memory section for storing the output of the above-mentioned offset detection section and the output of the movement direction detection section of the above-mentioned optical pickup as a pair, and an offset correction section for reading the output of the above-mentioned offset detection section corresponding to the output of the movement direction detection section of the above-mentioned optical pickup from the above-mentioned memory section and for correcting the offset of the above-mentioned tilt error signal.
The offset amount of the tilt error signal depending on the movement direction of the optical pickup is stored beforehand, the above-mentioned stored offset is read, and the tilt error signal is corrected depending on the movement direction of the optical pickup detected by the rotation direction detection section. Consequently, a tilt control error depending on the movement direction is prevented; when the disk is tilted, the tilt is controlled so that the light beam output from the optical pickup is perpendicularly applied to the disk 301 at all times. As a result, the stability of the information recording and reproducing apparatus can be improved greatly.
In order to record or reproduce information on the information tracks of a disk, an optical information recording and reproducing apparatus in accordance with the present invention from another point of view comprises an optical pickup for applying a light spot to the recording face of the above-mentioned disk via an object lens, a pickup movement section having a pickup movement motor for moving the above-mentioned optical pickup in a direction crossing the information tracks on the above-mentioned disk, an optical pickup movement direction detection section for detecting the movement direction of the above-mentioned optical pickup, a tilt error detection section, provided in the above-mentioned optical pickup and having a tilt sensor for detecting the tilt angle of the optical axis of the light beam of the optical pickup with respect to the above-mentioned disk face, for outputting a tilt error signal representing the above-mentioned tilt angle, a tilt drive section for tilting the above-mentioned optical pickup and the above-mentioned tilt sensor as an integrated unit, a tilt control section for controlling the above-mentioned tilt drive section depending on the above-mentioned tilt error signal, an offset detection section for detecting the offset of the above-mentioned tilt error signal, a temperature detection section disposed in the vicinity of the above-mentioned tilt sensor, a memory section for storing the output of the above-mentioned offset detection section, the output of the above-mentioned optical pickup movement direction detection section and the output of the above-mentioned temperature detection section as a group, and an offset correction section for reading the output of the above-mentioned offset detection section corresponding to the output of the above-mentioned optical pickup movement direction detection section and the output of the above-mentioned temperature detection section from the above-mentioned memory section and for correcting the offset of the above-mentioned tilt error signal.
The change amount of the offset with respect to an ambient temperature is measured beforehand, and both are stored in the memory section as a pair. When the apparatus is operated, the ambient temperature and the offset amount corresponding to the temperature are read from the above-mentioned memory section, and the offset of the tilt error detection circuit is corrected by using the read offset amount. Therefore, proper offset correction is carried out at all times even if the ambient temperature changes.
An optical information recording and reproducing apparatus in other aspect of the present invention comprises an optical pickup, including an object lens, for applying a light spot to the recording face of an optical disk on which information is recorded or reproduced on information tracks, a pickup movement section including a pickup movement motor for moving the above-mentioned optical pickup in a direction crossing the above-mentioned information tracks, a tilt error detection section for detecting the tilt amount of the optical axis of the light beam of the above-mentioned optical pickup with respect to the above-mentioned disk face and for outputting the tilt amount as a tilt error signal, a tilt drive section for tilting the above-mentioned optical pickup and the above-mentioned tilt detection section as an integrated unit, a tilt control section for controlling the above-mentioned tilt drive section depending on the above-mentioned tilt error signal so that the tilt amount conforms to a tilt control target value indicating a predetermined tilt amount, and a control target value change section for changing the control target value of the above-mentioned tilt control section.
By changing the control target value of the tilt control section, the optical pickup is maintained at an optimal tilt angle at all times, and the reliability during disk recording and reproduction is improved.
In order to record or reproduce information on the information tracks of a disk, an optical information recording and reproducing method in accordance with the present invention comprises a step of moving an optical pickup for applying a light spot to the recording face of the above-mentioned disk via an object lens in a direction crossing the information tracks on the above-mentioned disk, a step of detecting the movement direction of the above-mentioned optical pickup, a step of detecting the tilt of the optical axis of the light beam of the above-mentioned optical pickup with respect to the above-mentioned disk face and of outputting the tilt as a tilt error signal from the tilt error detection section, a step of tilting the above-mentioned optical pickup and the above-mentioned tilt error detection section as an integrated unit, a step of controlling the above-mentioned tilt drive section depending on the above-mentioned tilt error signal, a step of detecting the offset of the above-mentioned tilt error signal by using the offset detection section, a step of storing the output of the above-mentioned offset detection section and the output of the movement direction detection section of the above-mentioned optical pickup as a pair, and a step of reading the output of the above-mentioned offset detection section corresponding to the output of the movement direction detection section of the above-mentioned optical pickup from the above-mentioned memory section and of correcting the offset of the above-mentioned tilt error signal.
In order to record or reproduce information on the information tracks of a disk, an optical information recording and reproducing method in accordance with the present invention from another point of view comprises a step of moving an optical pickup for applying a light spot to the recording face of the above-mentioned disk via an object lens in a direction crossing the information tracks on the above-mentioned disk, a step of detecting the movement direction of the above-mentioned optical pickup, a step of detecting the tilt angle of the optical axis of the light beam of the optical pickup with respect to the above-mentioned disk face by using a tilt sensor provided in the above-mentioned optical pickup, a step of detecting a tilt error signal representing the above-mentioned tilt angle and of outputting the signal, a step (sic a step) of tilting the above-mentioned optical pickup and the above-mentioned tilt sensor as an integrated unit, a step of controlling the above-mentioned tilt drive section depending on the above-mentioned tilt error signal, a step of detecting the offset of the above-mentioned tilt error signal by using the offset detection section, a step of detecting the temperature in the vicinity of the above-mentioned tilt sensor, a step of storing the output of the above-mentioned offset detection section, the detection output of the movement direction of the above-mentioned optical pickup and the detection output of the above-mentioned temperature as a group, and a step of reading the output of the above-mentioned offset detection section corresponding to the detection output in the movement direction of the above-mentioned optical pickup and the detection output of the above-mentioned temperature from the above-mentioned memory section and of correcting the offset of the above-mentioned tilt error signal.
An optical information recording and reproducing method in accordance with the present invention from another point of view comprises a step of moving an optical pickup, including an object lens, for applying a light spot to the recording face of an optical disk, on the information tracks of which information is recorded or reproduced, in a direction crossing the above-mentioned information tracks, a step of detecting the tilt amount of the optical axis of the light beam of the above-mentioned optical pickup with respect to the above-mentioned disk face and of outputting the tilt amount as a tilt error signal, a step of tilting the above-mentioned optical pickup and the above-mentioned tilt detection section as an integrated unit, a step of controlling the above-mentioned tilt drive section depending on the above-mentioned tilt error signal so that the tilt amount conforms to a tilt control target value indicating a predetermined tilt amount, and a control target value change step of changing the control target value of the above-mentioned tilt control section